A first example of an imaging arrangement for use in this type of display is a barrier, for example with slits that are sized and positioned in relation to the underlying pixels of the display. In a two-view design, the viewer is able to perceive a 3D image if his/her head is at a fixed position. The barrier is positioned in front of the display panel and is designed so that light from the odd and even pixel columns is directed towards the left and right eye of the viewer, respectively.
A drawback of this type of two-view display design is that the viewer has to be at a fixed position, and can only move approximately 3 cm to the left or right. In a more preferred embodiment there are not two sub-pixel columns beneath each slit, but several. In this way, the viewer is allowed to move to the left and right and perceives a stereo image in his/her eyes all the time.
The barrier arrangement is simple to produce but is not light efficient. A preferred alternative is therefore to use a lens arrangement as the imaging arrangement. For example, an array of elongate lenticular elements can be provided extending parallel to one another and overlying the display pixel array, and the display pixels are observed through these lenticular elements.
The lenticular elements are provided as a sheet of elements, each of which comprises an elongate semi-cylindrical lens element. The lenticular elements extend generally in the column direction of the display panel, with each lenticular element overlying a respective group of two or more adjacent columns of display pixels.
In an arrangement in which, for example, each lenticule is associated with two columns of display pixels, the display pixels in each column provide a vertical slice of a respective two dimensional sub-image. The lenticular sheet directs these two slices and corresponding slices from the display pixel columns associated with the other lenticules, to the left and right eyes of a user positioned in front of the sheet, so that the user observes a single stereoscopic image. The sheet of lenticular elements thus provides a light output directing function.
In other arrangements, each lenticule is associated with a group of four or more adjacent display pixels in the row direction. Corresponding columns of display pixels in each group are arranged appropriately to provide a vertical slice from a respective two dimensional sub-image. As a user's head is moved from left to right, a series of successive, different, stereoscopic views are perceived creating, for example, a look-around impression.
Increasing the number of views improves the 3D impression but reduces the image resolution as perceived by the viewer, since all views are displayed at the same time by the native display. A compromise is typically found whereby a number of views (such as 9 or 15) are displayed in so-called viewing cones, and these viewing cones repeat across the field of view. The end result is a display with a large viewing angle, although viewers are not entirely free in choosing their location from which to view the 3D monitor or television: at the boundaries between viewing cones the 3D effect is absent and ghost images appear. This wide viewing angle is a problem in situations where the user of the display would prefer no eavesdropping on all or certain parts of the display content. One typical example is reading of mail and documents during commutes. It has been proposed to provide a display with private and public viewing modes. This has also been proposed for 3D autostereoscopic displays, for example in US-2011/0234605. This document discloses that different modes can be created by driving different arrangements of sub-pixels.